On Tue, Jun 23, 2026 at 4:15 AM Pavel Tikhomirov <[email protected]> wrote: > > The cachestat() syscall reads page cache statistics straight from the > file's f_mapping. Stackable filesystems such as overlayfs keep the data > pages in an underlying inode's mapping rather than in the overlay > inode's, so cachestat() reports all zeroes for them. > > Add a ->cachestat() file operation and route the syscall through a new > vfs_cachestat() helper that calls it when present, falling back to > file's f_mapping otherwise. This lets stackable filesystems forward the > query to the file that actually owns the page cache. No behaviour change > for regular files. > > Signed-off-by: Pavel Tikhomirov <[email protected]> > --- > Note: Memset change might be a bit tricky, I moved it to no > ->cachestat() path to avoid multiple memset on nested overlayfs, that > means that ->cachestat() is expected to be able to handle unitialized > cs.
nit: maybe a comment somewhere to document this? > --- > include/linux/fs.h | 10 ++++++++++ > mm/filemap.c | 43 +++++++++++++++++++++++++++++++++++-------- > 2 files changed, 45 insertions(+), 8 deletions(-) > LGTM otherwise. With Amir's suggestions incorporated: Acked-by: Nhat Pham <[email protected]>
